Babies which are born after about a 10-week gestation period typically are capable of functioning independently of the mother from a hormonal standpoint, and at this stage, the only maternal functions are to supply oxygen and nutrients to the fetus, and to remove waste byproducts, such as uric acid. However, until a gestation period of about 28 weeks, lungs are not sufficiently developed to support the baby; consequently, babies born before the 28th week, as by irreversible premature labor, have had little chance to survive.